Chemical vapor deposition (CVD) is the process of depositing a solid material from a gaseous phase onto a substrate by means of a chemical reaction. This deposition reaction is generally thermal decomposition, chemical oxidation, or chemical reduction. In one example of thermal decomposition, organometallic compounds are transported to the substrate surface as a vapor and are reduced to the elemental metal state on the substrate surface. For chemical reduction, the reducing agent most usually employed is hydrogen, although metal vapors can also be used. The substrate can also act as a reductant as in the case of tungsten hexafluoride reduction by silicon. The substrate can also supply one element of a compound or alloy deposit. The CVD process can be used to deposit many elements and alloys as well as compounds including oxides, nitrides and carbides.
In the present invention, thermal decomposition reactions are used to manufacture highly uniform deposits on semiconductor wafer substrates, e.g., coatings of polysilicon, and silicon nitrides formed by the dichlorosilane and ammonia process.
Chemical vapor deposition of electronic materials is described by T. L. Chu et al, J. Bac. Sci. Technol. 10:1 (1973) and B. E. Watts, Thin Solid Films. 18:1 (1973). They describe the formation and doping of epitaxial films of such materials as silicon, germanium and GaAs, for example. A summary of the chemical vapor deposition field is provided by W. A. Bryant, "The Fundamentals of Chemical Vapour Deposition", Journal of Materials Science. 12:1285 (1977). Low pressure CVD production of polysilicon deposits is summarized by Rosler, R. Solid State Technology. 63-70 (April 1977), the contents thereof being incorporated by reference.